The invention relates to a transmission, especially for motor vehicles, with at least two shafts, i.e. an input shaft, an output shaft, and in some cases a countershaft. The transmission has at least two or more pairs of gears, each pair consisting of a free gear and a fixed gear. The free gears have shift clutches by which they can be selectively coupled or uncoupled in rotation-locking engagement with a first shaft. The fixed gears are permanently tied to share the rotation of their shaft(s).
Transmissions of this kind are generally known in the field of automotive technology. They suffer from the draw back that they cannot transmit power during gear shifts. Consequently, there is an interruption in the tractive force when shifting gears to change the transmission ratio.
Furthermore, in vehicles with a transverse layout of the combustion engine, the axial space available for the power train is limited, which imposes severe design constraints on integrating an axially mounted electro-mechanical energy converter for generating electrical energy from kinetic energy and/or as a supplementary drive source. However, the use of electro-mechanical energy converters performing multiple functions is a desirable feature in modern power train concepts.
It is therefore the object of the present invention to improve the design of a transmission of the aforementioned kind and to optimize the spatial layout, so that an electro-mechanical energy converter can be integrated in the transmission to perform the functions of, e.g., a starter for the combustion engine, an electric generator, or a supplementary drive source. In the latter function, the electro-mechanical energy converter serves to eliminate or at least reduce the temporary loss in traction during gear shifts.
According to the invention, the foregoing objective is met by a transmission, specifically a shiftable gear transmission with at least two shafts, i.e., an input shaft, an output shaft, and in some cases a countershaft. The input shaft is driven by a combustion engine by means of a crankshaft. The transmission has two or more gear pairs and an electro-mechanical energy converter. The electro-mechanical energy converter has a rotor and a stator. At least one clutch in the transmission serves to couple the electro-mechanical energy converter to at least one of the shafts.
The rotor can be coaxially arranged on the input shaft, output shaft, or another shaft of the transmission, with a clutch between the rotor and the shaft. A second shaft may also be equipped to be coupled to the electro-mechanical energy converter through a clutch. The electro-mechanical energy converter can also have its own rotor shaft, running parallel to one of the transmission shafts, where the rotor shaft can be driven or can drive one of the transmission shafts, e.g., by way of one of the fixed gears or through a separate gear provided specifically for this purpose. Belt drives or chain drives, including those with an automatically variable ratio such as a continuously variable cone-pulley transmission, are especially advantageous. As a further possibility, the electro-mechanical energy converter could be coupled to a flywheel, particularly a flywheel of the combustion engine.
A transmission according to the invention can, in principle, include a shiftable gear transmission with at least two shafts, e.g., an input shaft, an output shaft, and in some cases countershaft. The transmission has at least two or more pairs of gears, each pair consisting of a first gear (also called free gear) and a second gear (also called fixed gear). The free gears have shift clutches or sliding sleeves by which they can be selectively coupled or uncoupled in rotation-locking engagement with a first shaft. The fixed gears are permanently locked to a second shaft. To change the transmission ratio, at least one of the shift clutches or sliding sleeves is designed to be moved automatically by an actuator, e.g., an electric motor, electro-magnet, or by a hydraulic or pneumatic device. A shift clutch can be a friction-locking or form-locking clutch. Shift clutches as well as sliding sleeves (which serve to couple and uncouple the connections of free gears to their shafts) can be equipped with appropriate synchronization means.
In a transmission according to the invention, it can further be of advantage if the electro-mechanical energy converter can be switched selectively between the at least two shafts, e.g., between the input shaft and the output shaft of the transmission. In another embodiment of the invention, only one shaft, i.e., either the output shaft or the input shaft of the transmission, is configured to be connectable to the electro-mechanical energy converter by means of a clutch that can be moved into and out of engagement by an automated actuator of the kind described above.
To contribute further to the solution of the problem targeted by the invention, the electro-mechanical energy converter can be operated in such a way that during a gear shift for changing the transmission ratio from one level to another, the electro-mechanical energy converter is used to reduce the temporary loss in vehicle traction by delivering a driving torque to the output shaft. For example, in a gear shift with the steps of disengaging the start-up clutch, shifting out of the current gear, shifting into the new gear, and re-engaging the start-up clutch, the electric motor generator can be activated at the point where the start-up clutch begins to slip, i.e., where it no longer transmits the full amount of the engine torque to the input shaft of the transmission. The decrease and loss of torque passing through the start-up clutch can be at least partially compensated by an increasing contribution of torque from the electro-mechanical energy converter. Since the time interval for a gear shift is very short, it can be advantageous if the electro-mechanical energy converter is designed for a nominal continuous-duty power capacity that is less than the peak amount of torque which has to be compensated during a gear shift. Thus, the electro-mechanical energy converter will be under a thermal overload during a short time interval, e.g., at up to 300% of nominal power capacity, but this has the advantage that the dimensions of the motor/generator can be kept at a minimum. The deployment of the torque generated by the electro-mechanical energy converter is advantageously controlled in a manner where the torque on the output shaft varies smoothly, e.g., in a linear or other continuous transition, from the torque level required with the previously engaged gear to the torque level required for the new gear level. Especially with motor/generators of very small dimensions, it can also be advantageous if the traction-supporting torque of the motor/generator available during the interruption in vehicle traction is kept smaller than the lesser of the torques required for the previous or new gear ratio, e.g., between 100% and 30%, but preferably between 100% and 50% of the torque needed for the gear that requires the lower amount of torque.
It is further advantageous, if the transmission input shaft can be connected to the crankshaft of the combustion engine, e.g., through a start-up clutch that is controlled either automatically by means of an actuator or manually. The start-up clutch can be a dry-friction clutch, laminar disc clutch, or a hydrodynamic clutch such as a hydrodynamic torque converter or a fluid coupling (also called Fottinger coupling) which in some cases may have a converter-bypass clutch. Also advantageous is a design where the start-up clutch is arranged on a dual-mass flywheel. The start-up clutch can be advantageously accommodated in the clutch bell housing between the combustion engine and the transmission, or it can be arranged inside the transmission. Furthermore, the clutch that connects the electro-mechanical energy converter to the input shaft can be configured as a dual clutch together with the start-up clutch, and it can likewise be accommodated in the clutch bell housing or in the transmission. In special applications, it can also be advantageous if the clutch that couples the electro-mechanical energy converter to the input shaft is arranged outside the transmission and the start-up clutch is omitted.
The different clutches, such as the start-up clutch, the clutches of the free gears, as well as clutches by which the electro-mechanical energy converter is coupled to the input or output shaft, are engaged and disengaged by actuators, as mentioned previously. In principle, it is possible to operate all or at least some, especially two, clutches by means of one appropriately designed actuator. For example, this could be an actuator controlling the clutches by way of a sliding valve piston which controls each clutch through a hydraulic or pneumatic device with at least one master cylinder and one slave cylinder, associated connecting conduits, as well as a pressure source. As another possibility, the actuator could be an electric motor acting on two or more clutches through appropriate linkage mechanisms. It is particularly advantageous to combine actuators for clutches that move in the same axis, engaging preferably in opposite directions or engaging with different amounts of axial displacement, such as dual clutches and/or the clutches or sliding sleeves that serve to engage the free gears of the transmission. As an example of a particularly advantageous arrangement, one actuator may be used for engaging and disengaging the clutches, while a second actuator is used to select the clutch or sliding sleeve that needs to be engaged in order to shift into the desired gear ratio. The latter arrangement is known per se from conventional manually or automatically shifted transmissions, e.g., transmissions laid out according to an H-pattern and shifted by means of two electric motors. In order to optimize the shift process, the actuators, especially electric motors or electro-magnets, may be equipped with a series-mounted reducing or magnifying gear mechanism.
An electro-mechanical energy converter arranged to act on the input shaft of the transmission can be used to start the combustion engine, if the clutch between the input shaft and the electro-mechanical energy converter is engaged. It is advantageous if the vehicle also has a start-up clutch and a flywheel mounted on the input shaft. This provides the benefit of using the momentum of a moving mass to start the engine by first accelerating the flywheel and then engaging the start-up clutch to let the built-up kinetic energy start the engine with or without the simultaneous support of the electro-mechanical energy converter. If the electro-mechanical energy converter is arranged to be coupled to the output shaft, then the connection to the input shaft can be made, e.g., through one of the gear pairs, with the start-up clutch engaged and the free gear of the gear pair disengaged from the output shaft.
The electro-mechanical energy converter can further be used as drive source to drive at least a part of the transmission, i.e., at least one gear level, e.g., first or reverse gear. The engageable connection between the input shaft and the output shaft can be made directly through the respective gear pair, and the gear that connects to the electro-mechanical energy converter can be a free gear that can be coupled to its shaft through a clutch.
In a further mode of operation, the rotor of the electro-mechanical energy converter can be driven by a part of the transmission, e.g., a gear pair of one of the shift stages, to convert mechanical kinetic energy into electrical energy, where the electrical energy could be delivered to a storage device, e.g., a battery with a high current rating. The kinetic energy can be provided by the combustion engine, e.g., while the vehicle is moving, or also when the vehicle is standing still and the transmission is running in neutral. A torque flow path from the combustion engine and the electro-mechanical energy converter can be established through a suitable combination of clutch settings, e.g., by engaging the start-up clutch and the clutch that connects the electro-mechanical energy converter to the input or output shaft.
A further use of the electro-mechanical energy converter is in the recovery of kinetic energy from slowing down the vehicle. This requires that a torque-flow path be made available between the electro-mechanical energy converter and the output shaft, e.g., by engaging a clutch between the output shaft and the electro-mechanical energy converter if the latter is arranged on the output shaft. If the electro-mechanical energy converter is arranged on the input shaft, the torque flow path between the input and output shaft can be established through a gear pair with a free gear that can be locked by means of a clutch or sliding sleeve. The electro-mechanical energy converter can have a gear on its rotor shaft that is rotationally coupled to the input-shaft gear of the aforementioned pair, with a clutch to couple and uncouple the torque-transmitting connection to the electro-mechanical energy converter. This arrangement allows the electro-mechanical energy converter to recover and store energy that would otherwise be lost as heat energy in the brakes or in working against the drag torque of the engine. It may be advantageous, depending on the amount of braking action required, to couple or uncouple the combustion engine by means of the start-up clutch.
The electro-mechanical energy converter can further be used as the sole source of drive power or as a supplementary drive source to support the combustion engine (booster function), where the start-up clutch is engaged, disengaged, or in slipping engagement depending on the desired drive mode.
The electro-mechanical energy converter can be integrated in the transmission, so that the rotational axis of the rotor is coaxial to the input shaft or output shaft of the transmission, or the rotor shaft of the electro-mechanical energy converter can ran parallel to the input or output shaft of the transmission.
In an advantageous embodiment, the transmission according to the invention can be arranged with transverse orientation in the front portion of the vehicle. Another embodiment can involve an advantageous lengthwise arrangement in the front portion of the vehicle. The transmission according to the invention can also be used in other advantageous power train layouts.
The actuators of the clutches or shifter elements in different embodiments are advantageously based on electric motors with rotary movement of an output element or electric motors with linear movement of an output element, including linear motors. It is also advantageous to use rotary hydraulic actuators (such as gear pumps, vane pumps, etc.), linear hydraulic actuators (such as piston/cylinder units, etc.), rotary pneumatic actuators (vane pumps, etc.), linear pneumatic actuators (pistons, etc.), piezo-electric actuators, and thermo-mechanical actuators.
An actuator can have force-amplifying mechanisms interposed between a motor and an actuating element, including, e.g., levers, wedges, cam-disc devices, threaded spindles, worm gears, spur gears, planetary gear sets, etc. Actuators can also work with hydraulic or pneumatic transmitting devices employing master cylinders and slave cylinders, or with pressure-medium based devices in general.
To drive the movement of the actuator-controlled element, motion-transmitting devices can be used to good advantage, including adjustable or self-adjusting transmitting devices, mechanical devices such as levers, pull ropes, rods, slides, wedges, curve-follower devices, etc.; or hydrostatic devices such as master/slave cylinders with or without sniffle bores, hydrodynamic and pneumatic devices.
The functions of several individual actuators for selecting and shifting gears in a gear-changing process can also be combined through the use of transmitting mechanisms. This makes it possible to shift more gear pairs than there are actuators. Examples for this are shift transmissions with an H-shaped shifting pattern or a shift-control cylinder which can shift between any number of gear levels with a single actuator. The clutches, including a start-up clutch as well as other clutches, can be of a conventional push- or pull-action design, where in a non-actuated state the clutch engagement is maintained by a spring-bias force of an energy-storing device. A clutch can further be of a force-reducing, self-adjusting type, in which the effect of wear, e.g., on the friction linings is automatically compensated. In a further embodiment, the clutch can be an actuator-engaged clutch whose engagement has to be maintained at least in part by an actuator force.
It is advantageous to include a torsional oscillation damper in the power train, e.g., with a spring damper unit between the engine and the start-up/shift clutch. The damper can be integrated in the clutch disc or in a dual-mass flywheel.
Sensors are arranged to monitor the rpm rates of the engine and the transmission. The output rpm rate of the transmission can also be calculated from the wheel rpm rates. It can further be advantageous, if an rpm sensor is arranged at the transmission input shaft.
A motor vehicle transmission according to the present invention may further include:
a control unit with microprocessor including signal-processing functions, electronics, control logic, signal amplifiers, data bus systems, etc.;
indicator systems such as warning light, acoustic warning device, shift-level indicator, etc.;
an operator-control element such as stick-shift lever, switch, etc.;
programs with selector elements for selecting between automatic shift, manual shift, winter mode, sport mode, individual driving habit adapter, etc.;
an electronic engine control unit with electronic fuel-injection control, such as the so-called E-gas feature, in the combustion engine (electro-motoric, electronic, or other operating principle);
a sensor arrangement for the detection of engine rpm rate, wheel rpm rate, vehicle doors not shut, hood not shut, etc.;
a data and control signal communication system between the transmission control unit and the engine control unit of the combustion engine.
With a transmission as described above, an electro-mechanical energy converter can be designed as an integral combination of starter motor, generator, alternator, starter/generator, decelerator/auxiliary drive source. It is advantageous if the electro-mechanical energy converter is of a type that performs functions including engine start, generating electricity for the on-board power system of the motor vehicle, and in some cases electrical braking to recover kinetic energy, in which case the surplus electrical energy is put back into the power train. The electro-mechanical energy converter can also be used to assist in synchronizing the transmission and to decelerate the transmission input shaft to zero when the vehicle is standing still. This offers the advantage that synchronizer rings can be omitted in some embodiments of the invention. The electro-mechanical energy converter can also be used advantageously to supply torque to the power train during shift phases in order to smooth out abrupt declines of the drive torque.
The electro-mechanical energy converter can apply torque to the combustion engine by acting on the flywheel. In the case of a dual-mass flywheel, the electro-mechanical energy converter can work on the primary or secondary flywheel. In another embodiment, it is advantageous if the electro-mechanical energy converter works or acts on the transmission input shaft, either in a coaxial or offset arrangement. The electro-mechanical energy converter can drive the combustion engine directly or through an intermediate gear mechanism. The intermediate gear mechanism can have a fixed or variable transmission ratio. It may be switchable between two or more fixed ratios, or the ratio may be variable in a continuous range without steps. The setting of a ratio may be performed under the control of a centrifugal device or by an actuator.
The rotary movement of the electro-mechanical energy converter can be transmitted to the engine shaft or to the transmission input shaft through the following rotation-transmitting elements:
Tooth-profiled gears (spur gear, bevel gear, etc.)
Endless-loop drives (chain, V-belt, gear belt, etc.)
Hydraulic drives (pump/motor, etc.)
The engine can be started, among other possibilities, in one of the following two ways. Either the electro-mechanical energy converter is used to accelerate the combustion engine directly, or the electro-mechanical energy converter is first brought up to speed independently and then coupled to the combustion engine, e.g. by engaging a friction clutch, in order to use the momentum of a higher rpm rate to start the engine. The latter kind of starting method can be performed through the start-up clutch after the electro-mechanical energy converter has first accelerated the input shaft of the transmission.
With transmissions according to the invention, it is possible to direct the full power of the electro-mechanical energy converter to the output side of the power train or to the input or output shaft of the transmission. Under different operating conditions of the transmission, it may also be enough to direct only a part of the full power of the electro-mechanical energy converter to the input or output shaft.
Arrangements are possible, where the electro-mechanical energy converter can be switched between the input shaft and the output shaft of the transmission.
The electro-mechanical energy converter can be operatively coupled to the input shaft of the transmission to perform one of the following: starting the combustion engine, generating electrical energy from kinetic energy of the engine or transmission, recovering energy, decelerating the rpm rate at the electro-mechanical energy converter (ratio change between the input and output shaft), setting the vehicle in motion with the electro-mechanical energy converter as drive source for the vehicle, boosting the propulsive power of the vehicle by using the electro-mechanical energy converter in tandem with the combustion engine, and moving the vehicle in reverse.
The electro-mechanical energy converter can be operatively coupled to the output shaft of the transmission to perform one of the following: filling the gap in vehicle traction during a shift phase of the transmission when, e.g., the start-up clutch on the input side is at least partially disengaged, generating electricity from kinetic energy of the engine or the transmission, recovering energy, decelerating the rpm rate at the electro-mechanical energy converter (ratio change between the input and output shaft), setting the vehicle in motion with the electro-mechanical energy converter as drive source for the vehicle, boosting the propulsive power of the vehicle by using the electro-mechanical energy converter in tandem with the combustion engine, and moving the vehicle in reverse.
In advantageous design variations, the electro-mechanical energy converter is arranged to act on:
a gear set for one of the forward speeds,
a gear on the input shaft,
a gear on the output shaft, or
the gear set for reverse drive.
The shift clutch of the gear set driven by the electro-mechanical energy converter can be advantageously configured as follows:
form-locking or friction-locking clutch at the gear on the input shaft, or
form-locking or friction-locking clutch at the gear on the output shaft.
A friction-locking clutch may be arranged with a gear on the input shaft and used as start-up clutch.
The actuators may be configured advantageously as electrically energized actuators or pressure-energized (hydraulic or pneumatic) actuators.
One actuator may be advantageously employed to actuate more than one shift clutch of the gear set of the electro-mechanical energy converter or to actuate all other shift elements, e.g., through a shift cylinder or a central shift-control shaft.
A torque-transmitting arrangement between the electro-mechanical energy converter and a gear stage of the transmission is advantageously configured:
as a direct-driving coaxial arrangement,
with a constant up/down ratio through an intermediate gear,
with a constant up/down ratio through a gear stage,
with a continuously variable transmission, or
with a step-shifting transmission.
Based on an estimate, the minimum power rating required in an electro-mechanical energy converter in a vehicle is nominally between 2 and 20 kW, preferably around 10 kW, assuming that the electro-mechanical energy converter can handle short-term overload conditions. If the electrically propelled driving mode is to be comparable to the combustion-powered mode and if, e.g., the first transmission level is to be replaced by an electrically powered speed level, it is practical to design the electro-mechanical energy converter for a nominal power of about 35 kW.
According to the inventive concept for the power train, the actuation of the start-up clutch and the shift transmission are automated. A control unit coordinates the functions and also regulates the electro-mechanical energy converter. The control unit communicates with other control devices of the vehicle, e.g., by way of a controller-area-network (CAN) bus.
The transmission control unit can be combined with other control units, e.g., of the combustion engine and the brake system (e.g., in the case of an electrical brake) and for the recovery of kinetic energy. The commands as to which operating mode is to be used and which gear is to be engaged may be dictated by a master control unit of the entire drive train.
If the power-steering system, the coolant pump and, if applicable, further auxiliary devices are operated electrically, the belt-drive(s) for these devices can be completely eliminated, whereby friction is reduced in the combustion engine.
The electro-mechanical energy converter has to be operable both as a motor and as a generator. To the extent possible and within the given capacity limit, the torque needs to be controllable independently of the rpm rate of the rotor through a voltage control, so that through an appropriate actuating means, the electro-mechanical energy converter can be set to run at the desired point of its operating characteristic (exciter field attenuation). It is also advantageous if the electro-mechanical energy converter has the capability to withstand short-term overload situations, because the operating modes as an engine starter and as a substitute drive source during traction gaps require a high power output only during short time intervals.
If the reverse gear of the shift transmission is to be replaced by a purely electrical reverse-drive mode, the electro-mechanical energy converter needs to be designed so that it can run in either sense of rotation, and the electronic power control must be capable of directing the flow of electric power accordingly.
Suitable types of power plants are externally excited machines such as reluctance motors, asynchronous motors, EC motors, DC shunt motors and, possibly, synchronous motors and stepper motors. The control capability of the machine should include its use as an energy-recovering brake.
The novel features that are considered as characteristic of the invention are set forth in particular in the appended claims. The improved apparatus itself, however, both as to its construction and its mode of operation, together with additional features and advantages thereof, will be best understood upon perusal of the following detailed description of certain presently preferred specific embodiments with reference to the accompanying drawing.